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Three New Studies on Sea Level Rise Bring New Concerns

Three new sea level rise studies published during the past week offer sobering lessons for coastal residents and policy makers, spelling trouble for portions of the East and West Coasts of the U.S.

The first lesson is that sea levels won’t rise at the same rate everywhere — in fact, some unlucky places are already seeing sea levels rise at rates that are dramatically faster than the global average. Specifically, the 600-mile stretch of coastline from North Carolina to Massachusetts is experiencing rates that are nearly three to four times higher than the global average, a trend that may continue during the coming decades.

This finding comes from a study published June 24 in the journal Nature Climate Change. The study makes clear that some of the most valuable real estate in the country, from the beaches of North Carolina to the posh Hamptons in Long Island, and including major cities such as New York and Boston, may see severe coastal flooding events much earlier than other parts of the country.

As Margaret Davidson, director of the Coastal Services Center for the National Oceanic and Atmospheric Administration (NOAA) in Charleston, South Carolina, told the Associated Press that the new research has “huge” implications.

“Somewhere between Maryland and Massachusetts, you've got some bodaciously expensive property at risk," she said.

The study, by researchers with the U.S. Geological Survey (USGS), emphasized that factors such as changing ocean currents, coastal land elevation fluctuations, and water temperature and salinity shifts in the North Atlantic Ocean are influencing the rate of sea level rise on the local level.

The study refers to the Cape Hatteras-to-Massachusetts stretch as a sea level rise “hotspot.” In this area, sea level has increased between 2 to 3.7 millimeters per year since about 1990, while the global increase during the same period was 0.6 to 1.0 millimeters per year.

“Ongoing accelerated sea level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast,” said Abby Sallenger, a USGS oceanographer and lead author of the study.

According to the Boston Globe, the study and others like it are prompting the city of Boston to require developers to take sea level rise into account when planning new development projects and take other climate change adaptation steps.

The USGS study is similar to a report on West Coast sea level rise that was published last week by the National Research Council. That report found that California stands to experience greater sea level rise impacts than other parts of the West Coast.

Climate Central’s research, entitled Surging Seas, shows that California, New York, and New Jersey have the third, fourth, and fifth largest populations on low-lying coastal land prone to sea level rise-driven coastal flooding issues, and New York City has the second largest population at risk of any city nationwide other than New Orleans.

Another paper from Nature Climate Change shows just how difficult it will be to avoid damaging amounts of sea level rise over the longer term unless greenhouse gas emissions are significantly slashed.

That study, by a research team in Germany, showed that even if global warming were limited to 2 degrees Celsius (3.6°F) compared to preindustrial times — a target that many policymakers and scientists now consider too difficult to achieve — global mean sea levels are likely to continue to rise during the next three centuries. On the bright side, the study found that emissions reductions that contain warming to 1.5°C (2.7°F) or below would “strongly” reduce sea level rise.

The researchers, led by Michiel Schaeffer of Climate Analytics and Wageningen University, found that if global average surface temperatures increase by more than 3°C, sea level rise could range between 6.6 and 16.4 feet by the year 2300, which would prove disastrous to many coastal population centers.

“. . . For New York City, it has been shown that 1 meter of sea level rise could raise the frequency of severe flooding from once per century to once every three years,” said study coauthor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research.

The study is the first long-term sea level rise projection that combines historical records of sea level rise during the past millennium with future scenarios for greenhouse gas emissions. It relied in part on estimates of the historical relationship between global average surface temperatures and global average sea level.